Which of the following tools is used to create gradients in Illustrator?

The Gradient tool in Adobe Illustrator is specifically designed to create and manipulate gradients. It allows users to apply color transitions smoothly from one color shade to another within shapes or along paths, giving designs depth and visual interest. When you select the Gradient tool, you can directly click and drag on an object to affect how the gradient is displayed, adjusting the direction and length of the gradient.

In contrast, the other tools mentioned serve different purposes. The Pen tool is primarily used for drawing precise paths and shapes. The Blend tool allows for the creation of smooth color transitions between two or more objects, which can create a blended effect but does not create gradients in the way the Gradient tool does. The Shape tool is used for creating geometric shapes like rectangles, ellipses, and polygons, but it does not deal with gradients directly. Therefore, the Gradient tool is uniquely suited for creating and adjusting gradient fills within your designs.